Bash scripting for arithmetic expression

Question

#!/bin/bash
x=10
echo x=$x
z=20
echo z=$z
y= expr $x + $z
echo y=$y

I want output like :

x=10
z=20
y=30

but it gives error like:

x=10
z=20
30
y=

y=`expr $x + $z` also works, looking for "Command Substitution in bash", is better Inian's solution way — Jose Ricardo Bustos M.
– Jose Ricardo Bustos M., Commented Jan 19, 2017 at 13:34

Inian · Accepted Answer · 2017-01-19 13:34:30Z

5

Do NOT use the outdated construct expr, use the arithmetic operator $(()) for POSIX compliant arithmetic in bash

y=$((x + z))
echo "y=$y"

answered Jan 19, 2017 at 13:34

Inian

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2 Comments

chepner Over a year ago

$((...)) is not just standard, but it performs the arithmetic in the current process, rather than starting a new process to run expr.

Jeffrey Cash Over a year ago

Additionally, you could replace y=$((x + z)) with ((y = x + z)) or simply y=x+z if you declare x, y and z as integers prior with declare -i x y z

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